Field of the Invention
The present invention relates to an ink jet recording apparatus, and particularly relates to means for maintaining a constant distance between a head and a recording medium.
As shown in FIGS. 5 and 6, conventionally a recording medium 17, such as a recording paper sheet or film, is wound around a platen 16 and is tensioned by a pair of pinch rollers 22a and 22b so that the recording medium 17 closely contacts the platen 16 to carry out printing.
However, in the conventional printing structure, a distance H between a nozzle tip 20 of a head 18 which ejects ink droplets and the recording medium 17 varies in the angular range of .+-..THETA. around the center line of platen 16. Further, in the multi-nozzle structure, the value of .THETA. is relatively great, so that H varies by a large amount, which causes degradation of print quality.
In ink jet recording, it is necessary to equalize as much as possible the distances from respective ones of an array of nozzle tips along the recording medium feeding direction (sub-scanning direction) to the face of the recording medium, and to minimize variations of traveling time of ink droplets in order to improve printing quality. When utilizing a head of the on-demand type, in order to compensate for the drawback of relatively low frequency of ink droplet production, multi-nozzle arrangements have been adopted. However, as noted above, it would be quite difficult to prevent degradation of printing quality without enlarging the platen diameter.